Production of fatty acids



Patented Aug. 1, 1933 UNITED STATES PATENT OFFICE and Heinrich Diekmann, Mannheim, Germany,

assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application July 11, 1931, Serial No. 550,274, and in Germany July 23, 1930 10 Claims.

The present invention relates to the production I of fatty acids by the destructive oxidation of hydrocarbons.

By the preparation of fatty acids by the destructive oxidation of difficultly volatile, from liquid to solid, paraffin hydrocarbons, i. e. those containing at least 8 carbon atoms, or mixtures consisting of such hydrocarbons or containing a preponderating quantity thereof, especially of paraffin wax, with the aid of air, oxygen, nitrogen oxides or nitric acid, an oxidation product is usually obtained which contains unsaponifiable constituents as well as the fatty acids. In order to separate the fatty acids from these constituents, which mainly consist of parafiins unoxidized or incompletely oxidized by the oxidation, i. e. to alcohols, aldehydes, ketones and other non-acid oxygen-bearing compounds, the crude oxidation product is usually saponified with aqueous solutions of alkaline agents and the solutionallowed to stand whereby the greater part of the unsaponifiable hydrocarbon 'constituents separates from the soap solution by reason of the formation of layers. The remainder of the unsaponifiable constituents must then be removed from the soap by extraction. For this purpose organic solvents of low boiling point, such as ligroin, benzine, acetone, ethyl alcohol, benzene or mixtures of these solvents have hitherto been employed.

We have now found that in the isolation of pure fatty acids from the said oxidation products it is advantageous to proceed in such a manner that after the saponification of the oxidation product, preferably after removal of that part of the unsaponifiable constituents which separates out from the soap solution without further treatment, the unsaponifiable constituents of the oxidation product which are dissolved or emulsified in the soap solutions are extracted with the aid of such hydrocarbons of high molecular weight (i. e. containing at least 8 carbon atoms), especially liquid or liquefied paraffins as have served as initial materials in the oxidation and may be subjected to oxidation and oxidized into fatty acids in mixture with the unsaponifiable constituents dissolved therein after the extraction.

The hydrocarbons of high molecular weight, especially paraffin waxes liquefied by heating, parafiin oil, middle oils from mineral oils or similar fractions from the destructive hydrogenation of oils or tars, as are suitable as initial materials for the oxidation have a specific solvent power for the unsaponifiable constituents and oils or mixtures of naphthenic acids with and may be readily separated from the soap solution again. Since that part of the unsaponifiable constituents which cannot be separated mechanically consists mainly of unoxidized and incompletely oxidized paraffins, it was not to be expected that they could be separated from the saponifiable constituents of the oxidation product with the aid of unoxidized hydrocarbons, even although it is known that natural fats mineral oil may be separated from the unsaponifiable constituents after saponification by shaking with solid paraflin wax while heating.

The process according to the present invention, contrasted with the usual extraction with solvents of low boiling point, has considerable practical advantages, because the latter must be freed from the unsaponifiable constituents dissolved therein by evaporation after the extraction while according to the present invention no evaporation is necessary. Thus neither is energy consumed for evaporation nor does evaporation loss take place because the mixture of unsaponifiable constituents and added parafiin wax obtained by the extraction may be 86 directly employed for the oxidation again.

The liquid soap solution itself, or the dry residue thereof, preferably after fine comminution, may be treated with the said hydrocarbons containing at least 8 carbon atoms in their molecule in order to effect extraction of the unsaponifiable constituents remained therein. During the extraction it is especially advantageous to employ elevated temperatures-or working with soap solutions at about the boiling 90 point depending on the melting point of the extracting agents which may be between 50 and, say, 110 C.and to work in stages on the usual counter current principle.

The following examples will further illustrate the nature of this invention but the invention is not restricted to these examples.

Example 1 kilograms of hard parafiin wax (having a 100 melting point of 52 C. and a specific gravity of 0.77 at 70 C.) are oxidized in a stirring autoclave in the usual manner at 70 C. with nitrogen oxides at a pressure of 5 atmospheres until the reaction product has a specific gravity of 0.88 at 70 C. and a content of 80 per cent of fatty acids and of 20 per cent of unsaponifiable matter. The oxidation product having a saponification value of 240 is saponified in a closed vessel at 200 C. with the aid of 120 kilograms of an aqueous 20 per cent solution 01' soda and then diluted with 220 liters of water. After the saponification about half the unsaponi'ilable constituents consisting mainly of paraffin wax separate in the form of an upper layer and are withdrawn. The remaining soap solution is stirred at about ll0 C. three times with 20 kilograms of paraiiin wax each time. The stirring on each operation is continued for an hour and the whole is then allowed to stand. The paraffin wax together with the unsaponifiable constituents dissolved therein forms a supernatant, easily separable layer and is withdrawn directly into the oxidation vessel.

The fatty acids precipitated, when the soap solution is acidified, only contain 2 per cent by weight of unsaponifiable constituents.

Example 2 An oxidation product of a soft paraffin wax (melting point 42 0.) prepared by oxidizing the said wax with nitrogen oxides at C. and at a pressure of i atmospheres and having a saponification value of 270 and a content of' 15 per cent of unsaponifiable constituents, is saponiiied, diluted with water and the soap solution separated from supernatant unattacked initial material as described in Example 1. The

soap solution then contains about 8 per cent (relative to the fatty acids contained therein in the form of soap) oi unsponifiable constituents dissolved or homogeneously emulsified in the soap solution. The solution is pumped to the top of an extraction towerfllled with filler stones having a diameter of from 5 to 25 millimeters through which tower the same paraffin wax as employed as the initial material for the oxidation, is passed in counter current after heating it to 90 C. At the bottom of the tower a soap solution is continuously drawn off which contains from 3 to 4 per cent only of unsaponifiable constituents calculated with reference to the fatty acids contained in the soap, the liquid paraifin wax enriched in oxygen-bearing unsaponifiable products of the oxidation being continuously drawn off at the top of the tower.

Example A distillate rich in paraffin and obtained by the destructive hydrogenation of American Mid- Continent oil is oxidized in any known manner with the aid of nitric acid whereby an oxidation product is obtained consisting of per cent of saponiiiable constituents and of 35 per cent of unsaponifiable constituents. After saponifying the oxidation product with aqueous 20 per cent caustic soda solution 390 parts of soap solution containing 120 parts of the oxidation product are diluted with 300 parts of water, separated from supernatant hydrocarbons and then stirred twice with 50 parts each of the aforesaid distillate for 2 hours at about 100 C. and the mixture is then allowed to settle. The distillate, enriched in the unsaponiflable constituents of the oxidation product which are dissolved in the soap solution, settles as a supernatant layer, is separated, and returned into the oxidation process. The fatty acids precipitated by acidifying the purified soap solution contain 6 per cent of unsaponifiable constituents in contrast with the original 35 per cent thereof.

What we claim is:-

1. In the production of fatty acids by the destructive oxidation of difiicultly volatile paraflin hydrocarbons, and saponiflcation of the resulting oxidation products, the step which comprises subjecting a resulting soap to extraction with a liquefied paraflin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

2. In the production of fatty acids by the destructive oxidation of dimcultly volatile parafiin hydrocarbons and saponification of the resulting oxidation products, the step which comprises subjecting an aqueous solution of the soap to extraction with a liquefied paraflln hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

3. In the production of fatty acids by the destructive oxidation of diiflcultly volatile paraffin hydrocarbons andsaponification of the resulting oxidation products, the step which comprises subjecting the soap, after drying, to extraction with a liquefied paraffin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

4. In the production of fatty acids by the destructive oxidation of diflicultly volatile parai'lln hydrocarbons and saponification of the resulting oxidation products, the step which comprises subjecting the soap at a temperature between 50 and about 110 C. to extraction with a liquefied paraffin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

5. In the production of fatty acids by the destructive oxidation of difiicultly volatile paraffin hydrocarbons, saponifioation oi. the resulting oxidation products and removal of unsaponifiable matter forming a supernatant layer on the resulting soap solution, the step which comprises subjecting the soap at a temperature between 50" and about 110 C. to extraction with a liquefied paraffin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

6. In the production of fatty acids by the destructive oxidation of a mixture of difiicultly volatile paraffin hydrocarbons comprising paraffin wax and saponification of the resulting oxidation products, the step which comprises subjecting the soap at a temperature between 50 and about 110 C. to extraction with a liquefied paraffin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

7. In the production of fatty acids by the destructive oxidation of paraffin wax and saponification of the resulting oxidation products, the step which comprises subjecting the soap at a temperature between 50 and about 110 C. to extraction with a liquefied parafin hydrocarbon material containing at least 8 carbon atoms in the molecule as has served as initial material in the oxidation.

8. In the production of fatty acids by the destructive oxidation of paraflin wax, saponification of the resulting oxidation products and removal of unsaponifiable matter forming a supernatant layeron the resulting soap solution, the step which comprises subjecting the soap solution at a temperature between 50 and about 110 C. to extraction with a liquefied paraffin hydrocarbon material containing at least a carbon atoms in the molecule as has served as initial material in the oxidation.

9. In the production of fatty acids by the destructive oxidation of paraflln wax, saponiflcation of the resulting oxidation products and removal of unsaponifiable matter forming a supernatant layer on the resulting soap solution, the

step which comprises subjecting the soap solu' tion at from to 100 C. to extraction with liquefied parafiin wax as have served as initial material in the oxidation.

10. In the production of fatty acids by the de- 

